James Webb has (already!) observed the most distant galaxy known to date

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The NASA space telescope has been making discoveries since its official commissioning on July 12. After stunning the world with incredible images of distant galaxies and the deepest image of the universe obtained to date, it now reveals the oldest galaxy ever observed. The data indicate that it appeared 300 million years after the Big Bang.

The first hundreds of millions of years of the universe (corresponding to a redshift, or redshift, greater than 10) mark an unexplored and mysterious time. Until now, only one galaxy had been discovered at this distance: the galaxy GN-z11, discovered in 2016 thanks to data from Hubble and Spitzer. Its redshift was already particularly high (z ≈ 11). One team set out to search for new galaxies of the same age or even earlier, using James Webb’s NIRCam.

In a non-peer-reviewed preprint paper, the researchers report the discovery of two “particularly bright” candidate galaxies, called GLASS-z13 and GLASS-z11 (with redshifts 13 and 11, respectively). Although it appears to us to be about 300 million years “only” after the Big Bang, GLASS-z13 becomes the most distant galaxy ever observed. The telescope only observes in the infrared, but the data has been “translated” into the visible spectrum: the galaxy is circular in shape, essentially red, but white in the center.

Look far to see into the past

We’re looking at potentially the most distant starlight anyone has ever seen Rohan Naidu, an astronomer at the Harvard Center for Astrophysics and first author of the paper, told AFP. In fact, just as we see our Sun as it was eight minutes ago (because its light takes about eight minutes to reach us), the light from the galaxy GLASS-z13 was emitted 13.5 billion years ago.

The GLASS-z13 galaxy in its stellar context. © Gabriel Brammer/Cosmic Dawn Center/Niels Bohr Institute/University of Copenhagen/AFP

Observing the formation of the very first galaxies after the Big Bang (13.8 billion years ago) is one of James Webb’s main objectives. We don’t yet know exactly when or how the earliest galaxies formed, and the new data captured by the instrument will undoubtedly provide some answers.

These are only preliminary data, but the researchers can already deduce some characteristics, some of which are surprising to say the least. To begin with, the two galaxies discovered are particularly massive: according to the team, they would have already accumulated about a billion solar masses in stars during the 300 to 400 million years after the Big Bang. This suggests that stars formed much earlier in the early universe and faster than scientists previously thought.

The team also points out that the luminosity of these galaxies (with an estimated UV absolute magnitude of -21) represents “a unique opportunity for detailed spectroscopic and morphological monitoring” at such a distance. Modeling of their morphology suggests that they are both disc-shaped. In particular, the nearest galaxy, GLASS-z11, shows a light profile that proves that its galactic disk was already firmly in place at z ≈ 11.

New Constraints on the Evolution of Primitive Galaxies

These galaxies appear relatively small: about 1600 light-years in diameter for GLASS-z13 and about 2300 light-years for GLASS-z11 (as a reminder, the diameter of our Milky Way is between 100,000 and 200,000 light-years). These dimensions are typical of bright galaxies usually seen at redshifts between 6 and 9, the researchers note.

These two objects are already imposing new constraints on the evolution of galaxies at the time of the cosmic dawn summarize the authors of the study. Their discovery is likely no coincidence, they say, adding that there is likely a whole population of ultraviolet light sources at this distance, with similar star-forming abilities.

If GLASS-Z13 existed at the beginning of the universe, its exact age is currently unknown. It could have appeared at any time during the first 300 million years. Of course, this discovery remains to be confirmed, but another team of astronomers – led by Marco Castellano of the National Institute of Astrophysics in Rome – working on the same data reached similar conclusions, which makes Naidu and his collaborators quite confident.

If these galaxies are confirmed by spectroscopy, and indeed two candidate galaxies with redshifts 11 to 13 remain to be detected in each small part of the extragalactic field (about 50 arcmin2), ” it is clear that JWST will succeed in pushing the cosmic limit to the edge of the Big Bang “, the researchers conclude.

Source: R. Naidu et al., arXiv

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